The present invention relates to plastic composite materials, which are polymers having grafted thereon rubbery polymers. The matrix phase polymer, such as polystyrene, is produced in the presence of the included rubbery phase polymer thus during this highly excited state the polystyrene is grafted onto the rubbery polymer.
The plastic composite materials have gained wide market acceptance as low cost engineering plastics. These materials exhibit exceptional impact strengths. The plastic composite materials generally are prepared by dissolving a rubber such as polybutadiene or SBR in the polymerization monomer, such as styrene. This mixture is then polymerized by means of thermal or free radical initiation to an intermediate degree of monomer polymerization, e.g., 20-30% conversion. The prepolymer thereby produced is then suspended in an aqueous medium and the polymerization continued to completion in suspension. The resultant graft composite is recovered, washed dried and extruded.
Although these composite materials are widely used, they have exhibited inferior stability to outdoor aging. Various techniques have been tried to improve stability, such as compounding with conventional stabilizers or attempting to select an improved combination of composite materials. In this latter regard, EPR has been substituted for SBR and polybutadiene as the rubber component. It is an advantage of the present invention that a graft copolymer of a thermoplastic material and rubber possessing improved stability has been discovered. It is a particular feature of the present invention that a single continuous copolymerization process has been devised. It is a particular advantage of the present invention that suitable graft copolymers can be produced by several variations of the general process for producing graft copolymers. It is a particular feature of the present invention that the graft copolymers produced have superior weather resistance. A particular feature of the present invention is the omission of a bulk polymerization in one embodiment thereof. These and other advantages and features will become apparent from the following discussion of the invention.